1. Field of the Invention
This invention relates generally to a voltage regulating device for a power generating system, and more specifically to a voltage regulating device for a power generating system which is required to be of smallest possible size and to have a high output, such as a portable engine generator, wherein the output can be fed to the load via the inverter, the supply voltage can be maintained at a constant level and the construction can be simplified to achieve cost reduction. 2. Description of the Prior Art
A description of an engine generator will be made in what follows as an example of this invention though it is not intended to limit the scope of this invention. An engine generator is usually constructed so that it can drive a load at 50 Hz or 60 Hz. In such an engine generator, a high output can be generated by increasing the revolution of the engine and/or increasing the field windings, as is well known. However, there is a limit in increasing the field windings. It may be fairly said, therefore, that the magnitude of output is determined by the revolution of the engine.
However, the output frequency of the generator itself is determined by the revolution of the engine. In a 2-pole generator, for example, which is directly connected to the engine, the revolution of the engine has to be set at 3,000 rpm in order to drive the load at 50 Hz, or at 3,600 rpm to drive the load at 60 Hz.
In a portable engine generator, for example, which is required to be of smallest possible size and yet to produce a high output, a construction has been devised in which higher output is obtained by setting the revolution of the engine at 5,000 rpm or 6,000 rpm, for example, and the rectified output is converted into the desired frequency, say, 50 Hz or 60 Hz using an inverter circuit. Moreover, in such an engine generator, a constant voltage control means is usually provided for maintaining supply voltage to the load as constant as possible.
However, in conventional engine generators having such a constant voltage control device and a multi-voltage changeover device to permit the generator to be used in various countries in the world, the constant voltage control device and the multivoltage changeover device are separately constructed. This often makes the construction relatively complicated, resulting in higher cost.